How do I eliminate background noise?

Okay I switched over 3 months ago and one reason was i was told I could record streaming, the other was the hassle of viruses.

No matter what I do I have not been able to eliminate background noises when I record streaming. I have tried with Audacity, and Amadeus Pro to record using the line in streaming but I am always picking up noises in the room.

This surprises me because of Mac's rep for sound quality and I was able to use a setting on windows which would only record the streaming audio and nothing in the room. I am not interesting in recording radio streams though I have tried a couple of streaming radio recorders.

Additionally I pick up a faint room echo which distorts the audio quality. I am sad to say at this point my windows did a far better job and think I must be missing something. Can anyone tell me how to do this? Thanks ~